Light emitting devices

ABSTRACT

Light emitting arrays in which the light source is positioned between two opposed reflector surfaces. The light from the source is reflected back past the source by a first reflector and then re-reflected by a second reflector back past the light source to the first reflector. A very thin assembly is obtained. The arrangement is particularly suitable for light emitting diodes and can be used for character displays.

United States Patent [191 K'osman et al.

[111 3,746,853 [451 July 17, 1973 1 LIGHT EMITTING DEVICES [75]Inventors: Karel Jan Williams Kosman;

Louis-Philippe Boivin; Dennis Effer, all of Ottawa, Ontario, Canada [73]Assignee: Bell Canada-Northern Electric Research Limited, Ottawa,Ontario, Canada [22] Filed: Mar. 10, 1972 [21] Appl. No.2 233,674

[52] US. Cl. 240/4l.35 D, 313/108 D [51] Int. Cl. F2lv 7/00 [58] Fieldof Search 240/41.35, 46.55, 240/41.35 D, 46.01, 46.33, 46.45; 313/117,108 D [56] References Cited UNITED STATES PATENTS 1,647,613 11/1927Fredette 240/46.55 1,954,978 4/1934 Aldrich 240/46.55

1,877,978 9/1932 Sarver 240/46.55 3,518,418 6/1970 Dubois 313/108 D X1,205,361 11/1916 Lakin 240/4l.35 B 3,676,668 7/1972 Collins et al....313/108 D 3,593,055 7/1971 Geusic 313/108 D 3,308,452 3/1967 Michel etal 313/108 D X Primary Examiner-Samuel S. Matthews AssistantExaminer-Richard M. Sheer Attorney-Sidney T. Jelly [57] ABSTRACT Lightemitting arrays in which the light source is positioned between twoopposed reflector surfaces. The light from the source is reflected backpast the source by a first reflector and then re-reflected by a secondreflector back past the light source to the flrst reflector. A very thinassembly is obtained. The arrangement is particularly suitable for lightemitting diodes and can be used for character displays.

3 Claims, 5 Drawing Figures Patented July 17, 1973 3 Sheets-Sheet 1Patented July 17, 1973 3 Sheets-Sheet 2 Fig. 4

Patented July 17, 1973 3 Sheets-Sheet m 6 om o O Q Q Q Q a Q a Q a Q a aU m U Q U 0 U 0 U U Q U a D a U Q U Q a u LIGHT EMITTING DEVICES Thisinvention relates to light emitting devices, and in particular thoughnot exclusively to light emitting devices as integers of a display, forexample for displaying numerals, letters and symbols, and also to suchdisplays.

Various forms of devices are used for the display of numerals, lettersand symbols in the so-called matchstick" style or code. It has beenproposed to use a small filament lamp for such a device. The light froma lamp is directed to a parabolic reflector, which reflects the lightback past the lamp to issue from a viewing face. Because of the shape ofthe reflector and other requirements such as a device is relativelylarge, being of a substantial thickness in the direction of lightemission from the size of the display. There is also the associateddisadvantage of the relatively high power consumption of a filamentlamp. Light emitting diodes have also been used, either with a pluralityof the diodes extending for the form of the segment, for example side byside, or with a diode mounted at the focus point of a parabolicreflector. The use of a plurality of diodes not only negates the lowpower consumption of individual diodes but may increase the powerconsumption above that of a filament lamp. Using a diode with aparabolic reflector means that the device has substantial thickness.

The present invention provides a device which is thin, has a very lowpower consumption and permits a reduction in the number of lightsources. In the broadest aspect the invention provides a light emittingdevice comprising a semiconductor light emitting element or diode havinga reflector on a first side and a reflective surface on a second side,light from the element being reflected by the reflector to thereflective surface and then reflected back past the element andreflector by the reflective surface. Particularly there is provided alight emitting device having a substrate onto which is positioned areflective layer. The reflective layer may be diffusing, and issubstantially flat. The light emitting element is mounted on thereflective layer and a reflector positioned over the element such thatlight from the element first passes to the reflector, the reflectorreflecting the light back to the reflecting layer. A light transmittingencapsulating material encapsulates the element and the reflectivesurface and the light is further reflected by the reflective layerthrough the encapsulating material to issue from a viewing surfacethereof.

For a segment of a display array, the reflector is arranged symmetricalto the element and has two portions arranged to reflect the light fromthe element back past the element, on either side of the element. Thereflective layer is flat and again reflects the light back past theelement to form a lighted segment on either side of the element.Conveniently the device is encapsulated with a black or non-lighttransmitting outer portion or frame and the light transmitting materialwithin the frame. The reflector can be mounted on the encapsulatingmaterial.

A display array is composed of a plurality of devices arranged in apredetermined pattern to meet the display requirements. The shape ofindividual devices can be varied to provide for effective assembly ofthe array.

The invention will be readily understood by the following description ofcertain embodiments, by way of 2 example, in conjunction with theaccompanying drawings, in which:

FIG. 1 is a plan view of a device;

FIG. 2 is a cross-section on the line II-lI of FIG. 1;

FIG. 3 is a plan view of a display using devices in accordance with theinvention;

FIG. 4 illustrates the conductor pattern and circuit for the arrangementof FIG. 3; and

FIG. 5 illustrates one form of multi-digit display using devices inaccordance with the present invention.

As seen in FIGS. 1 and 2 a light emitting device 10 comprises asubstrate 11 having a conducting layer or pattern 12 on which is mounteda semiconductor light emitting diode 13, hereinafter referred to as anLED, for example a gallium phosphide chip providing a p-n junction inthe known manner. In addition to acting as a conductor the layer 12serves as a reflective layer as will be described. The LED 13 isencapsulated in a light transmitting plastic material 14. Theencapsulating material is formed to provide sloping sides 15, the sidesinclined upwardly and inwardly relative to the substrate 11 and the LED13. Immediately over the LED 13 the encapsulating material is shaped asa trough 16 having sides 17 which incline upwards and outwards relativeto the LED 13, being on either side of the axis of the LED. A flat topsurface 18 acts as the surface through which light is emitted.

A layer of reflecting material 19 is formed on each of the sides 15 and17 so that a reflector is formed entirely around the periphery of theencapsulating material. On energization of the LED 13 light is emittedfrom the top 20 of the LED and from the sides 21. The light emitted fromthe top is reflected downwardly and outwardly to the layer 12. Layer 12,which conveniently is slightly diffusing, reflects the light upwards andlight will issue through the surface 18 on either side of the trough 16.Some light will be reflected by the layer 12 upwardly and outwardly forfurther reflection by the reflecting layer 19. Also light emitted fromthe sides 21 will be reflected by the layer 19, in this instancedownwards toward the reflective layer 12, and then upwards. The anglesof the various sides 15 and 17 are chosen so that the distribution ofthe light emission from the surface 18 is approximately even to providean appearance of uniform illumination at differing viewing angles. Atypical value for angle 0, the inclination of the sides 15 isapproximately 74, and for angle dz, the inclination of the sides 17 ofthe trough 16, is approximately 32. Any light emitted from the LED 13 isreflected repeatedly until it issues through the surface I8. Theencapsulating material 14 is usually of clear plastic material, whichcan be coloured and can also contain a small addition of a lightdiffusing filler. Paths of rays are indicated by lines 22.

The reflecting layer 12, as previously stated, is conveniently part ofthe conducting layer or pattern for the LED 13 and, for example, is ofgold.

FIGS. 1 and 2 illustrate a single light emitting device which can beused whenever a lighted device is required. Although shown as having theLED 13 mounted centrally with light issuing through two areas, one oneach side of the central trough 16, the LED can be mounted at one end ofa device to present one lighted area. Further, the particular shape ofthe device and particularly the shape or shapes of the area or areasthrough which light issues can be varied to suit requirements.

FIG. 3 illustrates an array or display using light emitting devices inaccordance with the present invention, the array being one which can bearranged to produce characters, in the present example figures. Asshown, a plurality of devices 30 are arranged in the form of a rectanglewith a central transverse bar. The positions of the LEDs are indicatedby the dotted circles 31 while the surfaces through which light issuesare indicated at 32. A decimal point is produced by a device 33 which issingle ended, that is, the LED indicated by the dotted circle 34 is atone end of the device, the light issuing surface indicated at 35. Bysuitable energization of particular LEDs it will be seen that figuresand letters can be produced.

An array, as for example illustrated in FIG. 3, is made as a completeunit. For example the individual devices 30 are themselves encapsulatedin a black plastic material. Either the black material can be mouldedhaving cavities formed for the eventual filling with the lighttransmitting plastic encapsulating the LEDs or, alternatively, the LEDsare first encapsulated in the light transmitting plastic to form theindividual devices and the devices are positioned in a mould and theblack plastic material moulded around the devices. If the black materialis first moulded, the reflecting layers 19 are formed by deposition byany suitable process on the related surfaces before the lighttransmitting plastic material is moulded into the black moulding. Whenthe individual devices are first moulded the reflecting layers 19 arethen deposited on the related surfaces prior to encapulsation into theblack material. Other colours than black can be used, the main intentionbeing to provide contrast.

The array for a character is generally mounted on a common substrate,which can be of ceramic for exam ple. The substrate will then usuallyform the substrate 11 as in FIG. I. A plan view of such a substrateshowing the conductor circuitry is illustrated in FIG. 4. In this figurethe devices are not shown, for clarity, but the positions of thesurfaces through which light issues are indicated at 32, as in FIG. 3.Similarly the positions of the LEDs are indicated at 31 and 34 as inFIG. 3.

As seen in FIG. 4 the ceramic substrate is at 40. A layer of conductingmaterial, for example gold, is deposited at 41. The LEDs 31 and 34 aremounted directly onto the gold layer. The conducting material 41 isdeposited in such a pattern that conductors 42 are formed, separatedfrom the main layer 41 by spaces 43. Connections are made to the LEDsfrom the conductor pattern 42 by leads 44. An MOS decoder/driver 45 isalso mounted on the gold layer 41 and is connected to the conductorpattern 42.by leads 46.

A multiple array is shown in FIG. 5, comprising five character arrays 50and a positive, negative and overflow array 51. A fixed decimal point isprovided at 52 but it will be appreciated that a device for a decimalpoint can be provided at each character array, fora movable decimalpoint.

In the arrays described and illustrated, seven devices are used for eacharray. For a larger character size a larger number of devices can beused, for example nine. Also differing arrangements ofthe devices can beused to provide arrays capable of differing or more complex characters.

Although devices in accordance with the invention have been described inuse for the production of character arrays, other uses exist for suchdevices, either used singly or in multiplicity. Devices can be mountedon a printed circuit board instead of a ceramic substrate, and can be acomponent ofa printed circuit device.

The devices in accordance with the invention are very thin. A characterarray as in FIGS. 3 and 4 can be produced with overall dimensions ofapproximately 0.25 ins. X 0.20 ins. and with a thickness from thesubstrate of approximately 0.020 ins. Individual devices have overalldimensions of approximately 0.120 ins. X 0.050 ins. by 0.020 ins. thick.These devices in accordance with the invention are thinner thanconventional devices. The use of LEDs reduces the power requirements ascompared with conventional devices, using other forms of light source.What Is claimed is:

l. A light emitting device for producing widely dif fused lightcomprising:

a substantially planar substrate having a reflecting surface thereon;

a semiconductor light emitting element mounted on the reflecting surfaceof said substrate, said light emitting element emitting light laterallyin a direc tion parallel to said substrate and forwardly in a directionnormal to said substrate;

a body of encapsulating material enclosing said light emitting element,said body of encapsulating material having a front surface and at leastone side surface, said side surface being tapered inwardly from saidsubstrate to said front surface;

a layer of reflecting material on the side surface of said body ofencapsulating material for reflecting the laterally emitted light fromsaid light emitting device downwardly onto the reflecting surface ofsaid substrate;

a layer of reflecting material on a portion of the front surface of saidbody of encapsulating material, said layer of reflecting material onsaid portion of said front surface being substantially in alignment withsaid light emitting element and being tapered inwardly from said frontsurface toward the reflecting surface of said substrate to reflect theforwardly directed light downwardly onto the reflecting surface of saidsubstrate;

the remaining portion of the front surface of said body of encapsulatingmaterial being light emitting to allow emission of the light reflectedby the re fleeting surface of said substrate.

2. A light emitting device claimed in claim 1, said inwardly taperedlayer of reflecting material on said portion of said front surfacecomprising two intersecting reflecting surfaces.

3. A light emitting device as claimed in claim I including an electricalconductor pattern on said substrate, the reflecting surface of saidsubstrate comprising part of said electrical conductor pattern.

i i 1 4 l

1. A light emitting device for producing widely diffused lightcomprising: a substantially planar substrate having a reflecting surfacethereon; a semiconductor light emitting element mounted on thereflecting surface of said substrate, said light emitting elementemitting light laterally in a direction parallel to said substrate andforwardly in a direction normal to said substrate; a body ofencapsulating material enclosing said light emitting element, said bodyof encapsulating material having a front surface and at least one sidesurface, said side surface being tapered inwardly from said substrate tosaid front surface; a layer of reflecting material on the side surfaceof said body of encapsulating material for reflecting the laterallyemitted light from said light emitting device downwardly onto thereflecting surface of said substrate; a layer of reflecting material ona portion of the front surface of said body of encapsulating material,said layer of reflecting material on said portion of said front surfacebeing substantially in alignment with said light emitting element andbeing tapered inwardly from said front surface toward the reflectingsurface of said substrate to reflect the forwardly directed lightdownwardly onto the reflecting surface of said substrate; the remainingportion of the front surface of said body of encapsulating materialbeing light emitting to allow emission of the light reflected by thereflecting surface of said substrate.
 2. A light emitting device asclaimed in claim 1, said inwardly tapered layer of reflecting materialon said portion of said front surface comprising two intersectingreflecting surfaces.
 3. A light emitting device as claimed in claim 1including an electrical conductor pattern on said substrate, thereflecting surface of said substrate comprising part of said electricalconductor pattern.